In an image forming apparatus such as an electrophotographic apparatus and electrostatic recording apparatus, an electrostatic latent image formed on a photoconductive member is first developed with a toner. After the toner image formed is then transferred to a transfer medium such as paper or OHP film, the transferred toner image is fixed thereto by any of various methods such as heating, pressing and use of solvent vapor.
On the transfer process, since the toner partly remains on the photoconductive member, it is necessary to remove the residual toner from the photoconductive member. A cleaning process for removing the residual toner from the photoconductive member after the transfer process includes a developing-spontaneously cleaning method (a cleaner-less method) for removing the residual toner on the photoconductive member without using a cleaning device, and another cleaning method using a cleaning device such as a cleaning blade and the like. And, such the image forming apparatus has mainly employed a pulverized toner which is produced in such a manner that a thermoplastic resin including a colorant, a charge control agent and the like is melt-blended for uniform dispersion and then the dispersion is subjected to pulverizing and classification.
Currently, the image forming apparatus is becoming more and more advanced and thus achievement of high speed as well as high resolution by a method of forming an electrostatic latent image by a laser is demanded. Accordingly, in addition to achieving a small particle diameter and a sharp particle diameter distribution for responding to the high resolution requirement, toners are required to have low-temperature fixing ability so as to correspond with high-printing speed model printers. However, the above-mentioned method for producing a pulverized toner has a difficulty for producing a toner having a particle diameter of about 5 to 6 μm or less and a limitation for designing a particle size distribution narrow at the classification process.
In order to solve such the problems, a toner producing method using a polymerization method has been proposed. The toners produced by the polymerization method are excellent in flowability and transferring ability for transferring onto a transfer medium. However, the polymerized toner adheres to a photoconductive member with a large adhesion force, so that the polymerized toner is easily passed through a space between the photoconductive member and the cleaning blade, thereby to cause cleaning failure.
Accordingly, generally, an additive referred to as an external additive is externally added to the surface of the colored resin particle. For the external additive, an inorganic fine particle is used typically.
For instance, Japanese Patent Application Laid-Open Hei 5-224456 discloses a developer comprising a toner for developing an electrostatic latent image including at least a binder resin and a colorant, and a spherical silica particle produced by a deflagration method. The literature shows that the developer is excellent in flowability, cleaning properties and the like. However, the toner disclosed in the literature causes lowering of cleaning properties due to printing over a long period of time, resulting in contamination of a photoconductive member and generation of fog on printed image.
Japanese Patent Application Laid-Open 2001-281911 proposed by the inventers of the present invention discloses a toner including an organic fine particle and an inorganic fine particle each having an average particle diameter and a sphericity within a specific range, respectively. And, Japanese Patent Application Laid-Open 2001-281918 proposed by the inventors discloses a toner including a silicate compound having a degree of hydrophobicity, a number average particle diameter and a sphericity within a specific range, respectively. The toners in both literatures can provide an image having high image density without fog and blur even if recycled papers are used. Beside that, a toner causing less fog and improved in cleaning properties are required.
Japanese Patent Application Laid-Open 2002-318467 discloses a toner to which an external additive is added, in which the external additive comprises a fine particle charged with an opposite polarity of the toner and having a particle diameter within a specific range, a monodisperse spherical silica having a gravity and a particle diameter within a specific range, respectively, and an organic compound having a diameter smaller than the monodisperse spherical silica. The literature further discloses that an image forming apparatus using the disclosed toner does not cause degradation of image quality and can prevent cleaning failure. However, since a toner comes to be used under a high-temperature and humidity condition recently, a toner causing less fog and improved in cleaning properties even under various humidity and temperature conditions is required.    Published Patent literature 1: Japanese Patent Application Laid-open Hei 5-224456,    Published Patent literature 2: Japanese Patent Application Laid-open 2001-284911,    Published Patent literature 3: Japanese Patent Application Laid-open 2001-281918,    Published Patent literature 4: Japanese Patent Application Laid-open 2002-318467.
Accordingly, the object of the present invention is to provide a toner, causing less fog and having excellent cleaning properties.